Increasing TCP's Initial Window

Status:

As the
official minutes of the
TCP Implemention Working Group (tcpimpl)
meeting show, at the December 1997 meeting
at the Washington IETF, there was rough consensus to allow
an initial window of two segments. At the March 1998
meeting at the L.A. IETF, there was a rough consensus
to allow an initial window of three or four packets (depending
on the segment size) for experimental purposes.

RFC 2581,
the April 1999 Proposed Standard on
TCP Congestion Control, says the following:
``IW, the initial value of cwnd, MUST be less than or equal to 2*SMSS
bytes and MUST NOT be more than 2 segments.''

Shepard, T., and Partridge, C.,
When TCP Starts Up With Four Packets Into Only Three Buffers
.
RFC 2415, Experimental, September 1998.
This paper explores TCP's behavior in a configuration with a 9600 bps
modem and only three packet buffers before the modem. The simulations in
this report show that a four-packet initial window does not
degrade the performance of a long-lived TCP connection.

The proposal from the internet draft has been implemented in the
ns
simulator. The test suite for this (at the moment, this test suite
only includes tests for one-way TCP) can be run with the command
"./test-all-tcp-init-win" in the directory "tcl/test".